1. Field of The Invention
The present invention relates generally to the field of orthodontics, particularly to the manufacture of orthodontic appliances. The present invention also relates to a system, program product, and related methods for designing and manufacturing orthodontic appliances for the purpose of straightening the teeth of a patient and custom precision brackets made in accordance with the methods.
2. Description of the Related Art
Orthodontic treatment applied to straighten or align teeth of a patient dates back hundreds of years. The treatment generally included use of wires wrapped around the patient's teeth. At around the mid-1970s, chiefly due to improvements in adhesive technology, the preferred method shifted to bonding brackets directly onto the teeth and running elastic wires of rectangular cross-sectional shape through slots in the bracket. Typically, the brackets are off-the-shelf products. In most cases, they are adapted to a certain tooth, for instance an upper canine, but not to the individual tooth of a specific patient. The adaptation of the bracket to the individual tooth is generally performed by filling the gap between tooth surface and bracket surface with adhesive to thereby bond the bracket to the tooth such that the bracket slot, when the teeth are moved to a finish position, lies in flat horizontal plane. The driving force for moving the teeth to the desired finish position is provided by the archwire. For lingual brackets, a system has been developed by Thomas Creekmore, for example, that has vertical bracket slots. This allows an easier insertion of the wire. The longer side of the wire is therefore oriented vertically.
The wires used in orthodontic treatment today are also generally off-the-shelf products. If they need to be individualized by the orthodontist, the goal is to do so with as few modifications as possible. According to such methodology, the brackets are designed in a manner so that at the end of treatment, when teeth are aligned, the bracket slots are supposed to be located and oriented in a planar manner. This means that a wire that would run passively through the slots, without applying any force, would be planar (flat). This treatment regimen is known as “straight wire.” The further the archwire is away from the tooth surface, the more difficult it is to achieve a precise finishing position for each tooth. An error of only 10 degrees, for example, in torque (rotation around the wire axis) may well induce a vertical error in tooth position of more than 1 mm. Thus, recognized by Applicant is the need for a precision brackets slot positioned as close to the tooth surfaces as possible which, in conjunction with a customized archwire, can form a precision archwire-bracket slot interface to thereby minimize torque error.
Another problem in orthodontics is to determine the correct bracket position. At the time of bonding, teeth may be oriented far away from the desired position. So the task to locate the brackets in a manner that a flat planar archwire drives teeth to the correct position requires a lot of experience and visual imagination. The result is that at the end of treatment a lot of time is lost to perform necessary adjustments to either bracket position or wire shape. This problem can be solved by creating an ideal setup, either virtually using three-dimensional scan data of the dentition or physically by separating a dental model of the dentition into single teeth and setting up the teeth in a wax bed in an ideal position. For example, U.S. Pat. No. 6,648,640 by Rubbert et al., titled “Interactive Orthodontic Care System Based On Intra-Oral Scanning of Teeth,” describes a wire-based approach to orthodontics based on generic brackets and a customized orthodontic archwire. The archwire can have complex twists and bends, and as such is not necessarily a flat planar wire. This patent document also describes a scanning system for creating three-dimensional virtual models of a dentition and an interactive, computerized treatment planning system based on the models of the scanned dentition. As part of the treatment planning, virtual brackets are placed on virtual teeth and the teeth moved to a desired position by a human operator exercising clinical judgment. The three-dimensional virtual model of the dentition plus brackets in a malocclused condition is exported to a rapid prototyping device for manufacture of a physical model of the dentition plus brackets.
U.S. Pat. No. 6,776,614 by Wiechmann et al., titled “Modular System for Customized Orthodontic Appliances,” describes a wire-based approach to orthodontics based on customized orthodontic brackets and a customized orthodontic archwire. This patent document further describes designing the brackets on a computer as a combination of three-dimensional virtual objects including a virtual bracket bonding pad and a virtual bracket body retrieved from a library of virtual bracket bodies. The virtual brackets can be represented as a file containing digital shape data and can be exported to a rapid prototype fabrication device.
Recent developments in orthodontics include the use of rapid prototyping technology to form the brackets. Rapid prototyping machines can be used for models of the brackets which are then used to form molds to form the brackets. These molds generally have a cavity defining the bracket and can have a channel forming a pathway to pour bracket-forming material into the mold. Solidified bracket-forming material remaining in the channel forms a runner which must be removed. Also, if the bracket slot is not formed as part of the molding process, a bracket slot must be cut into the bracket body.
Various methodologies of forming the bracket slot can include casting, grinding or milling. For example, WO94/10935 by Andreiko et al. titled “Custom Orthodontic Appliance Forming Method and Apparatus” describes forming brackets by cutting custom slots in bracket blanks while preserving the base inclination angle, or alternatively, inclining the bracket bases or pads; and forming bracket bases either contoured to conform to the surfaces of the teeth or interfaced with a bonding agent to fill the space between the bracket base and the tooth. Andreiko et al., although primarily describing forming the brackets using a mechanical cutter blade, also introduces without further elaboration that other means such as wire electrical discharge machining, machining, casting, or stereo lithography, may be employed.
Such methodologies are deficient in describing systems, apparatus, or methods for creating a highly-precise bracket slot, creating an undercut in the sidewalls of the bracket slots, cutting an investment cast bracket off a runner, or cutting a highly precise tube into the bracket body. Although the desire for precision brackets has been noted in Weichmann, D, “A New Bracket System for Lingual Orthodontic Treatment, Part 2: First Clinical Experiences and Further Development,” J. Orofac Orthop (2003), there has not been recognition, until now by the Applicant, of the need for a system, apparatus, program product, and methods of forming enhanced precision bracket slots or tubes using electrical discharge machining technology having such desirable features.